Powder metallurgy is a common manufacturing process used to produce components of high quality for applications, including vehicular engines. Powder metallurgy is often employed in the manufacture of engine components because it is economical, flexible and can produce a finished part that requires much less machining or secondary processing than other methods of forming components. Powder metallurgy allows for a component to be formed of a wide variety of alloys, composites, and other materials to provide the finished component with desirable characteristics. Moreover, powder metallurgy allows the porosity of a part to be controlled for lubricant impregnation. Powder metallurgy is well suited to manufacture parts of a wide range of sizes and shapes. Also, powder metallurgy can reliably produce parts with consistent dimensions and advantageous physical properties.
The powder metallurgy manufacturing process is often employed to form engine components. However, no examples of a piston, formed homogeneously or non-homogeneously, by a powder metallurgy forging process are known. Such a piston would provide substantial benefits in the industry over the present forged steel and cast aluminum pistons.
The art of making pistons is old and crowded. Nonetheless, considerable inventive effort continues to the present in order to form pistons having advantageous characteristics. A recent example is U.S. Pat. No. 6,435,077, issued Aug. 20, 2002, to Damour et al. The Damour reference discloses an integral, unitary piston wherein the pin bosses are carefully formed in order to permit a working tool to be inserted between the two bosses in order to form a relatively large cavity beneath the center post of the combustion chamber formed in the crown of the piston. It would be advantageous to form a piston that minimized the amount of machining that was necessary subsequent to initial formation of the piston in order to achieve the desired shape.
A second recent example of piston technology found in U.S. Pat. No. 6,279,455, issued Aug. 28, 2001, to Kruse. The Kruse reference discloses a piston in which the crown has an upper portion and a lower portion formed separately and then joined along specific faces to form a two piece crown of the piston. It would be advantageous to form a suitable piston in a single operation to minimize the complexity of suitably joining two portions of the crown and yet achieve a satisfactory piston structure.